This application claims the priority of German patent document 101 53 237.7, filed Oct. 31, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a process for automatically determining the modulation transfer function (MTF) of a focal plane array (FPA) camera and a system for its implementation.
Various measuring methods are known for determining the MTF, for example, from Vollmershausen and Driggers, “Analysis of Sampled Imaging Systems”, Bellingham, Wash., 2000. Traditional techniques require static imaging of a test structure onto the detector plane.
One object of the invention is to provide a system that can measure the modulation transfer function MTF of a focal plane array (FPA) camera in real time. Such a system is particularly advantageous in the case of a moving camera or moving scenery, or when measuring the residual stabilization error while exciting vibrations.
This and other objects and advantages are achieved by the method and apparatus according to the invention, for automatically determining the MTF of an FPA camera, in which a test grid is used to generate a beat whose amplitude corresponds to that of the grid image to be measured, without the sampling MTF. The image of the test grid has a spatial frequency in the detector plane that is detuned with respect to the Nyquist frequency of the detector array. The test grid covers a range of at least half a beat period, and then, regardless of the actual phase position, the modulation amplitude is determined therefrom. Comparative MTF measurements are thereby permitted without being affected by the sampling effect of an FPA, and particularly the MTF measurement in real time, which is suitable for application to moving images.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.